Individuals exhibit a high degree of variability in response to agents such as drugs, pharmaceutical compounds, and chemicals. The development of a drug or pharmaceutical compounds can take many years and cost millions of dollars. In addition, some companies use animals (e.g., mice, rabbits, dogs, cats, pigs, etc.) to test the efficacy and toxicity of drugs and/or pharmaceutical compounds to obtain data for Phase I trials. Many drugs that are being developed do not proceed beyond a Phase I trial for many different reasons. One plausible reason is a lack of data in an accepted animal model for the disease or symptoms which the drug is targeted to treat. Animals used in various disease models include, but are not limited to dogs, pigs, rabbits, cats, chimpanzees, and other primates. In addition, animals are used to test toxicity levels and toxicological responses to drugs and pharmaceutical compounds under development.
In animals, toxicity of a drug can be determined by observing several in vivo parameters, including but not limited to drug levels in blood, tissues, urine, and other biological fluids; enzymatic levels in tissues and organs; protein or sugar levels in blood and other biological fluids; elevation or depression in number, size, morphology, and/or function of cells (e.g., white blood cells, lymphocytes, red blood cells, etc.), tissues, or organs (e.g., liver, heart, kidney, etc.). Other physical and physiological parameters which may be useful include but are not limited to survival rate of animals, appearance (e.g., hair loss, brightness of eyes, etc.), and behavior (e.g., eating habits, sleeping habits, etc.).
With the advent of molecular and recombinant technology, genetic and molecular analysis provides another method by which toxicity may be measured. Differential gene expression technology involves detecting the change in gene expression of cells exposed to various stimuli. The stimulus can be in the form of growth factors, receptor-ligand binding, transcription factors, or exogenous factors such as drugs, chemicals, or pharmaceutical compounds. Differential gene expression can be observed by using techniques involving gel electrophoresis and polynucleotide microarrays.
A polynucleotide microarray may include genes for which full-length cDNAs have been accurately sequenced and genes which may be defined by high-throughput, single-pass sequencing of random cDNA clones to generate expressed sequence tags (ESTs). Bioinformatic algorithms such as Unigene group cDNA clones with common 3′ ends into clusters which tentatively define distinct human genes. An ideal cDNA microarray might therefore contain one representative from each Unigene cluster. In practice, given the current complement of about 45,925 Unigene clusters, most microarrays contain at most one-third of the total Unigene set.
Researchers focused on detecting changes in expression of individual mRNAs can use different methods to detect changes in gene expression, for example, microarray, gel electrophoresis, etc. Other methods have focused on using the polymerase chain reaction (PCR) and/or reverse transcriptase polymerase chain reaction (RT-PCR) to define tags and to attempt to detect differentially expressed genes. Many groups have used PCR methods to establish databases of mRNA sequence tags which could conceivably be used to compare gene expression among different tissues (See, for example, Williams, J. G. K., Nucl. Acids Res. 18:6531, 1990; Welsh, J., et al. Nucl. Acids Res., 18:7213, 1990; Woodward, S. R., Mamm. Genome, 3:73, 1992; and Nadeau, J. H., Mamm. Genome 3:55, 1992). This method has also been adapted to compare mRNA populations in a process called mRNA differential display. In this method, the results of PCR synthesis are subjected to gel electrophoresis, and the bands produced by two or more mRNA populations are compared. Bands present on an autoradiograph of one gel from one mRNA population, and not present on another, correspond to the presence of a particular mRNA in one population and not in the other, and thus indicate a gene that is likely to be differentially expressed. Messenger RNA derived from two different types of cells can be compared by using arbitrary oligonucleotide sequences of ten nucleotides (random 10-mers) as a 5′ primer and a set of 12 oligonucleotides complimentary to the poly A tail as a 3′ “anchor primer”. These primers are then used to amplify partial sequences of mRNAs with the addition of radioactive deoxyribonucleotides. These amplified sequences are then resolved on a sequencing gel such that each sequencing gel has a sequence of 50-100 mRNAs. The sequencing gels are then compared to each other to determine which amplified segments are expressed differentially (See, for example, Liang, P. et al. Science 257:967, 1992; See also Welsh, J. et al., Nucl. Acid Res. 20:4965, 1992; Liang, P., et al., Nucl. Acids Res., 3269 1993; and U.S. Pat. Nos. 6,114,114 and 6,228,589).
The process of isolating mRNA from cells or tissues exposed to a stimulus (e.g., drugs or chemicals) and analyzing the expression with gel electrophoresis can be laborious and tedious. To that end, microarray technology provides a faster and more efficient method of detecting differential gene expression. Differential gene expression analysis by microarrays involves nucleotides immobilized on a substrate whereby nucleotides from cells which have been exposed to a stimulus can be contacted with the immobilized nucleotides to generate a hybridization pattern. This microarray technology has been used for detecting secretion and membrane-associated gene products, collecting pharmacological information about cancer, stage specific gene expression in Plasmodium falciparum malaria, translation products in eukaryotes, and a number of other scientific inquiries. See, for example, Diehn M, et al. Nat Genet. 25(1):58-62 (1993); Scherf, U., et al. Nat Genet. 24(3):236-44 (1993); Hayward R. E., et al. Mol Microbiol 35(1):6-14 (1993); Johannes G., et al. Proc Natl Acad Sci U S A 96(23):13118-23 (1993). Microarray technology has also been used in exploring drug-induced alterations in gene expression in Mycobacterium tuberculosis. See, for example, Wilson M., et al. Proc Natl Acad Sci. 96(22):12833-8 (1999). The use of microarray technology with animal genes, e.g., canine genes, during drug development to detect drug-induced alternation in vertebrates, such as dogs, would provide a method that is fast, efficient, cost-effective and could spare many animals from being the subjects of laboratory tests.
The discovery and/or characterization of a set of toxicologically relevant genes would be useful in simplifying the development, screening, and testing of new drugs. While some genes are known to be differentially displayed in response to one agent, a more useful tool for assessing toxicity is a panel of genes which are identified as toxicologically relevant genes. The invention provided herein fulfills these needs and provides disclosure to novel canine genes as well.
The disclosure of all patents and publications cited herein are hereby incorporated by reference in their entirety.